Defects in oxidative phosphorylation. Biochemical investigations in skeletal muscle and expression of the lesion in other cells

Mitochondria are very vulnerable to genetic and environmental damage. If a patient is suspected of having a mitochondrial disease, elevated blood lactate, lowered blood free carnitine, abnormal urinary organic acids and carnitine esters and tissue histopathology may help with the diagnosis. For biochemical assessment of the defect, muscle is the tissue of choice even when involvement of other organs like heart or brain is more prominent.We have studied isolated muscle mitochondria and homogenates from muscle biopsies in 250 patients, and have detected in more than one third mitochondrial defects in oxidative phosphorylation, dehydrogenases, non-redox enzymes catalyzing synthesis of fuel molecules and in the carnitine system. Several patients showed more than one defect.We have selected eight patients to illustrate how a relatively simple series of investigations in both isolated mitochondria and homogenate can be used for the identification of defects in oxidative phosphorylation in a small amount of muscle (200 mg or more). Identification of the defect(s) is important since it may provide the basis for rational treatment. A minority of the patients recovered partly or completely, which is unique in treatment of inborn errors of subcellular organelles.An important aspect of mitochondrial dysfunction is the tissue specificity. The defect may be systemic but is often clinically expressed in only one or a few tissues. Rarely, tissue-specific defects can be understood on the basis of tissue-specificity of mitochondrial (iso-)enzymes. Mitochondrial deficiencies of all biotin enzymes and most CoA-linked enzymes are expressed in fibroblasts; most respiratory chain defects are not.When mitochondrial ATP synthesis has been compromised by a mitochondrial defect, secondary lesions may be generated by changes in mitochondrial protein synthesis, activated proteases and phospholipases, increased matrix CoA and resulting carnitine deficiency, decrease in Krebs cycle intermediates and increased free radical formation and lipid peroxidation.     

The variability of hemolysis in the cold agglutinin syndrome

The amount of lysis effected by cold agglutinins is directly related to the ability of the antibody to initiate complement activation. This ability is modified by the concentration of antibody, its thermal amplitude (the highest temperature at which the antibody will react with the cell), the degree to which antibody fixation is modified by the presence of complement components (particularly C3) on the membrane, and the degree to which antibody, once fixed, is able to fix the components of complement. In vitro measurement of these factors correlates with the rate of hemolysis in vivo.     

Immunophenotypic analysis of reticulocytes in paroxysmal nocturnal hemoglobinuria

The hematologic disorder paroxysmal nocturnal hemoglobinuria (PNH) occurs following an acquired somatic mutation in the Piga gene within a bone marrow stem cell. The progeny of this mutated cell cannot synthesize glycosylphosphatidylinositol (GPI) anchors, with a resultant deficiency in surface expression of all GPI-linked proteins. The protean clinical manifestations of PNH presumably result from the deficiency of these GPI-linked surface proteins. To explain the observation that neutrophils are affected at a significantly higher percentage than circulating erythrocytes and to analyze the proliferative rates of erythroid production in PNH, we studied 25 patients using flow cytometry. The fluorescent dye thiazole orange was used to detect reticulocytes, and CD59 monoclonal antibody was used to identify GPI-deficient cells. In contrast to the mature circulating erythrocytes, the percentage of abnormal reticulocytes was similar to the percentage of affected neutrophils. However, the vast majority of reticulocytes was completely GPI-deficient, ie, were type III cells, even in patients with only modest numbers of circulating type III erythrocytes. In addition, greater than 5% type II reticulocytes were identified in only 3 patients, although greater than 5% type II mature erythrocytes were identified in 10 of 25 patients. The results show that the erythroid and neutrophil bone marrow precursors have an equivalent proliferative advantage in PNH. The data also have important implications for the origin of type-II erythrocytes in PNH.     

Minactivin expression in human monocyte and macrophage populations

Adherent monolayer cultures of human blood monocytes, peritoneal macrophages, bone marrow macrophages, and colonic mucosa macrophages were examined for their ability to produce and secrete minactivin, a specific inactivator of urokinase-type plasminogen activator. All except colonic mucosa macrophages produced and secreted appreciable amounts of minactivin, but only blood monocytes were stimulated by muramyl dipeptide (adjuvant peptide) to increase production. The minactivin from each of these populations could be shown to preferentially inhibit urokinase-type plasminogen activator and not trypsin, plasmin, or "tissue"-type plasminogen activator (HPA66). A plasminogen-activating enzyme present in monocyte cultures appeared unaffected by the presence of minactivin and could be shown to be regulated independently by dexamethasone.     

Purification and properties of heparin-releasable lipoprotein- associated coagulation inhibitor

The lipoprotein-associated coagulation inhibitor (LACI) is present in vivo in at least three different pools: sequestered in platelets, associated with plasma lipoproteins, and released into plasma by intravenous heparin, possibly from vascular endothelium. In this study we have purified the heparin-relesable form of LACI from post-heparin plasma and show that it is structurally different from lipoprotein LACI. The purification scheme uses heparin-agarose chromatography, immunoaffinity chromatography, and size-exclusion chromatography and results in a 185,000-fold purification with a 33% yield. Heparin- releasable LACI (HRL), as analyzed by sodium dodecyl sulfate- polyacrylamide gel electrophoresis, under reducing conditions, appears as a major band at 40 Kd and a minor band at 36 Kd. Immunoblot analysis suggests that the 36-Kd band arises from carboxyl-terminus proteolysis that occurs during the purification. HRL has a specific activity similar to that of HepG2 or lipoprotein LACI. HRL and lipoprotein LACI combine with lipoproteins in vitro while purified HepG2 LACI does not. I125-labeled HRL, injected into a rabbit, is cleared more slowly than I125-labeled HepG2 LACI, which may be due to attachment to lipoproteins in vivo. Preliminary evidence suggests that HRL is associated with vascular endothelium, possibly by attachment to glycosaminoglycans.     

The biochemical and clinical consequences of 2'-deoxycoformycin in refractory lymphoproliferative malignancy

A deficiency of adenosine deaminase, an enzyme important in purine nucleoside catabolism, is associated with a severe combined immunodeficiency disease in children. Inhibition of this enzyme in vitro and in vivo results in an impairment in lymphoblast proliferation. We have investigated the pharmacologic inhibition of this enzyme by 2'-deoxycoformycin in 15 patients with hematologic malignancies. Biochemical consequences of the administration of this agent were closely monitored in erythrocytes, nucleated peripheral blood and bone marrow cells, serum, and urine. A marked rise in erythrocyte dATP was accompanied by a depletion of ATP in those patients exhibiting toxicity. Most patients excreted large amounts of deoxyadenosine but not adenosine in the urine. Serum deoxyadenosine rose in patients demonstrating a marked decrease in cell mass. The biochemical disturbances and clinical toxicity, including hepatic, renal, and conjunctival abnormalities, were usually reversible. Central nervous system toxicity, which potentially was the most serious consequence, was associated with high erythrocyte dATP/ATP ratios and high levels of cerebrospinal fluid deoxyadenosine. In patients with lymphoma and leukemia, objective responses were observed but were short- lived. Patients with chronic lymphocytic leukemia receiving weekly low doses of the drug demonstrated minimal toxicity and some efficacy. The chemotherapeutic potential o 2'-deoxycoformycin, as either a single agent or in combination with Ara-A, merits further exploration.     

Association between physical performance characteristics and independence in activities of daily living in middle‐aged and elderly men

Aim: Functional status at one moment in time is a determinant of future functional status and survival. Physical deterioration tends to occur early in the disabling process; however, etiological questions remain. This study investigated the association between physical performance characteristics and functioning independently in middle‐aged and elderly men. Methods: A total of 400 independently‐living men aged 40–80 years were included in this cross‐sectional study. Preservation of function was measured using the Stanford Health Assessment Questionnaire. Physical characteristics were muscle strength and power by dynamometer, lung function, lower extremity function by physical performance score, and physical activity by Voorrips‐questionnaire. Logistic regression analysis was used to estimate the association between potential determinants and the dichotomized Health Assessment Questionnaire score. The odds ratios (OR) were adjusted for age, body mass index, education, socioeconomic status, smoking, alcohol and number of chronic diseases. Results: After adjustment for confounders, higher walking speed (OR = 2.96, 95% CI 1.31–6.72) and shorter time to carry out the chair stand test (OR = 0.84, 95% CI 0.76–0.94) were associated with a higher probability of being independent in activities of daily living (ADL). Borderline significant associations were found for higher lung function and higher leg strength with higher probability of being independent in ADL. No associations were found for grip strength, physical performance score, standing balance and physical activity. Conclusion: Lower body function and lung function were associated with a higher probability of being independent in ADL. Geriatr Gerontol Int 2013; 13: 274–280 .     

X-linked ataxia,weakness, deafness,and loss of vision in early childhood with a fatal course

An X-linked recessive disease with, in almost all patients, a fatal course in early childhood, occurring in a five-generation family is described. The 12 affected boys had early-onset floppiness, ataxia, liability to infections especially of the upper respiratory tract, deafness, and later, a flaccid tetraplegia and areflexia. Eleven boys died before the age of 5 years. One boy is still alive at the age of 12 years, but in addition to the above-mentioned signs, he must be ventilated at night and is nearly blind due to optic atrophy. In the only patient whose central nervous system could be examined at the time of autopsy, an almost complete absence of myelin in the posterior columns of the spinal cord was found. This may be the main pathological substrate for the neurological findings. No biochemical or immunological defects were detected. The family also counted 16 healthy male siblings and 13 definite of 28 possible female carriers. Some carriers developed a hearing impairment in early adulthood. As far as is known now, this disease has not been described before.     

Significance of centro-temporal spikes on the EEG

In a prospectively studied group of 43 children with centro-temporal spikes on the EEG, only 26 had the classical epileptic syndrome related to this EEG abnormality. Ten patients never had epileptic manifestations. In the other seven cases two types of epileptiform activity were encountered: in addition to the centro-temporal spikes generalized spike-and-wave complexes or - in other patients - occipital epileptiform phenomena occurred. In these cases the clinical signs and symptoms correlated best with the non-Rolandic EEG abnormalities. Some patients had only a few centro-temporal spikes during the recording of the EEG; in others this epileptiform activity was almost continuously present. This quantitative difference had no clinical correlation. Centro-temporal spikes should probably be looked upon as an (epi)phenomenon of cerebral disfunction with a wide range of clinical and electroencephalographic expressions.